Rubber composition and tires made by using the same

ABSTRACT

The rubber composition of the present invention is prepared by mixing 10 to 200 parts by mass of silica and 1 to 30 parts by mass of a silane compound having sulfur atom, which has a specific structure such that an organooxysilyl group is present at both ends of the molecule and sulfide or a polysulfide is present at the central portion of the molecule, with 100 parts by mass of a polymer. The rubber composition of the present invention has a small viscosity in the unvulcanized condition and provides excellent dispersion of silica. When this composition is used as a material for a tire tread, a tire exhibiting excellent abrasion resistance, a small rolling resistance and excellent braking property and steering stability on wet roads, can be obtained.

TECHNICAL FIELD

The present invention relates to a rubber composition comprising asilane compound having sulfur atom and a specific structure, moreparticularly, to a rubber composition exhibiting excellent abrasionresistance, a small rolling resistance and excellent braking propertyand steering stability on wet roads when the rubber composition is usedas a tire tread, and to a tire using the rubber composition.

BACKGROUND ART

Among various fillers used for rubber compositions, silica has drawbacksin processability although silica provides a small rolling resistanceand excellent braking property and steering stability on wet roads. Forexample, it is necessary that a multi-stage mixing be conducted due to agreat viscosity in the uncured condition. Silica has other drawbacks inthat dispersion of the filler is poor, vulcanization is delayed, andstrength at break and abrasion resistance are markedly decreased (forexample, Japanese Patent Application Laid-Open No. Heisei8(1996)-176345).

When silica is mixed with rubber, it is widely conducted to overcome theproblems that a coupling agent is added so that the viscosity in theuncured condition is decreased and the modulus and the abrasionresistance are improved. However, this process has a problem in that thecoupling agent is expensive, and the cost of production increasesdepending on the formulation.

It is also conducted that an additive for improving dispersion is usedto improve the processability by decreasing the viscosity in the uncuredcondition through improvement in the dispersion of silica. However, thisprocess has a drawback in that abrasion resistance decreases. When astrongly ionic compound is used as the agent for improving dispersion,processability such as adhesion to rolls occasionally decreased.

DISCLOSURE OF THE INVENTION

The present invention has an object of providing a rubber compositionwhich has a small viscosity in the unvulcanized condition, providesexcellent dispersion of silica and exhibits excellent abrasionresistance, a small rolling resistance and excellent braking propertyand steering stability on wet roads when the rubber composition is usedas a material for a tire tread and a tire using the rubber composition.

As the result of extensive studies by the present inventors to overcomethe above problems, it was found that the above object could be achievedby the rubber composition and the tire described in the following. Thepresent invention has been completed based on this knowledge. Thus, thepresent invention provides:

-   (1) A rubber composition which comprises, per 100 parts by mass of a    polymer, 10 to 200 parts by mass of silica and 1 to 30 parts by mass    of a silane compound having sulfur atom represented by average    structural formula (I):    (R¹O)_(3-p)(R²)_(p)Si—R³—S_(m)—R⁴—S_(m)—R₃—Si(R²)_(p)(OR¹)_(3-p)  (I)    wherein R¹ and R² each represent a hydrocarbon group having 1 to 4    carbon atoms, R³ represents a divalent hydrocarbon group having 1 to    15 carbon atoms, p represents an integer of 0 to 2, m represents a    number of 1 or greater and smaller than 4, which may be an average    of numbers, and R⁴ represents a divalent functional group    represented by one of following general formulae (II) to (IV):    S—R⁵—S  (II)    R⁶—S_(x)—R⁷  (III)    R⁸—S_(y)—R⁹—S_(x)—R¹⁰  (IV)    wherein R⁵ to R¹⁰ represents a linear or branched divalent    hydrocarbon group having 1 to 20 carbon atoms, a divalent aromatic    group or a divalent organic group having a hetero atom which is not    sulfur atom or oxygen atom, R⁵ to R¹⁰ may represent a same group or    different groups, and x, y and z each represent a number of 1 or    greater and smaller than 4, which may be an average of numbers;-   (2) A rubber composition described in (1), wherein a purity of the    silane compound having sulfur atom is 60% or greater at a time when    the silane compound having sulfur atom is mixed to form the rubber    composition;-   (3) A rubber composition described in any one of (1) and (2),    wherein, at a time when the silane compound having sulfur atom is    mixed to form the rubber composition, a content of silane compounds    having sulfur atom and three or more silicon atoms in one molecule    is 30% by mass or smaller of the rubber composition;-   (4) A rubber composition described in any one of (1) to (3), wherein    a BET surface area of the silica is 40 to 350 m²/g;-   (5) A rubber composition described in any one of (1) to (4), wherein    the polymer is a diene-based rubber;-   (6) A tire which comprises a member comprising a rubber composition    described in any one of (1) to (5); and-   (7) A tire described in (6), wherein the member is a tire tread.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

A rubber composition which comprises, per 100 parts by mass of apolymer, 10 to 200 parts by mass of silica and 1 to 30 parts by mass ofa silane compound having sulfur atom represented by average structuralformula (I):(R¹O)_(3-p)(R²)_(p)Si—R³—S_(m)—R⁴—S_(m)—R₃—Si(R²)_(p)(OR¹)_(3-p)  (I)In above average structural formula (I), R¹ and R² each represent ahydrocarbon group having 1 to 4 carbon atoms, R³ represents a divalenthydrocarbon group having 1 to 15 carbon atoms, p represents an integerof 0 to 2, m represents a number of 1 or greater and smaller than 4,which may be an average of numbers, and R⁴ represents a divalentfunctional group represented by one of following general formulae (II)to (IV):S—R⁵—S  (II)R⁶—S_(x)—R⁷  (III)R⁸—S_(y)—R⁹—S_(x)—R¹⁰  (IV)In above general formulae (II) to (IV), R⁵ to R¹⁰ represents a linear orbranched divalent hydrocarbon group having 1 to 20 carbon atoms, adivalent aromatic group or a divalent organic group having a hetero atomwhich is not sulfur atom or oxygen atom, R⁵ to R¹⁰ may represent thesame group or different groups, and x, y and z each represent a numberof 1 or greater and smaller than 4, which may be an average of numbers.

The silane compound having sulfur atom which is used in the presentinvention is a compound represented by average structural formula (I)and has organooxysilyl groups at both ends of the molecule and sulfideor a polysulfide at the central portion of the molecule.

In the structural formula, R¹ and R² each represent a hydrocarbon grouphaving 1 to 4 carbon atoms such as methyl group, ethyl group, n-propylgroup, i-propyl group, n-butyl group, i-butyl group, t-butyl group,vinyl group, allyl group and isopropenyl group. R¹ and R² may representthe same group or different groups. R³ represents a divalent hydrocarbongroup having 1 to 15 carbon atoms such as methylene group, ethylenegroup, propylene group, n-butylene group, i-butylene group, hexylenegroup, decylene group, phenylene group and methylphenyl-ethylene group.p represents an integer of 0 to 2, and m represents a number of 1 orgreater and smaller than 4, which may be an average of numbers. As forthe numbers giving the average represented by m, it is sufficient thatthe average represented by m is within this range. The silane compoundmay be a mixture of a plurality of silane compounds having sulfur atomin which the number as the basis for the average represented by m isdifferent among the compounds. From the standpoint of the effect of thepresent invention which will be described below, it is preferable that mrepresents a number of 1 or greater and smaller than 2. It is morepreferable that m represents 1.

R⁴ in structural formula (I) represents a divalent functional grouprepresented by any one of the above general formulae (II) to (IV). Fromthe standpoint of the effect of the present invention which will bedescribed below, it is preferable that R⁴ represents a divalentfunctional group represented by general formula (IV).

R⁵ to R¹⁰ represents a linear or branched divalent hydrocarbon grouphaving 1 to 20 carbon atoms, a divalent aromatic group or a divalentorganic group having a hetero atom which is not sulfur atom or oxygenatom. Examples of the group represented by R⁵ to R¹⁰ include methylenegroup, ethylene group, propylene group, n-butylene group, i-butylenegroup, hexylene group, decylene group, phenylene group,methylphenylethylene group and groups derived from these groups byintroducing a hetero atom which is not sulfur atom or oxygen atom suchas nitrogen atom and phosphorus atom into these groups. In any one ofgeneral formulae (II) to (IV) representing the functional grouprepresented by R⁴ in structural formula (I), R⁵ to R¹⁰ may represent thesame group or different groups. From the standpoint of the effect of thepresent invention which will be described below and the cost ofproduction, it is preferable that R⁵ to R¹⁰ each represent hexylenegroup.

It is essential that the group represented by R⁴ has sulfur atom. x, yand z each represent a number of 1 or greater and smaller than 4, whichmay be an average of numbers. From the standpoint of the effect of thepresent invention which will be described below, it is preferable thatx, y and z each represent a number of 2 or greater and smaller than 4and more preferably 2 or greater and 3 or smaller, which may be anaverage of numbers.

From the standpoint of the effect of the present invention, it ispreferable that the purity of the silane compound having sulfur atom is60% or greater, more preferably 70% or greater and most preferably 80%or greater at the time when the silane compound having sulfur atom ismixed to form the rubber composition.

The silane compound having sulfur atom which is used in the presentinvention occasionally contains polymers such as a dimer and a trimer ofthe compound represented by structural formula (I) which are producedduring the production. Silane compounds having sulfur atom and three ormore silicon atoms in one molecule such as the polymers described aboveoccasionally adversely affect the effect of the present invention. Inthe present invention, it is preferable that, when the silane compoundhaving sulfur atom is mixed to form the rubber composition of thepresent invention, the content of the silane compound having sulfur atomand three or more silicon atoms in one molecule is 30% by mass orsmaller, more preferably 10% by mass or smaller and most preferablysubstantially zero percent of the rubber composition at the time.

In the present invention, the silane compound having sulfur atom ismixed in an amount of 1 to 30 parts by mass per 100 parts by mass of apolymer. From the standpoint of the effect of the present inventionwhich will be described below, it is preferable that the silane compoundhaving sulfur atom is mixed in an amount of 2 to 20 parts by mass.

The polymer used in the present invention is not particularly limited aslong as the rubber composition can be formed. It is preferable that thepolymer is a diene-based rubber. Specifically, natural rubber andvarious types of diene-based synthetic rubbers can be used. Thediene-based synthetic rubbers are more preferable. Examples of thediene-based synthetic rubber include butadiene-based polymers such aspolybutadiene (BR), copolymers of butadiene and aromatic vinyl compoundsand copolymers of butadiene and other diene-based monomers;isoprene-based polymers such as polyisoprene (IR), copolymers ofisoprene and aromatic vinyl compounds and copolymers of isoprene andother diene-based monomers; butyl rubber (IIR); ethylene-propylenecopolymers; and mixtures of these rubbers. Among these rubbers,butadiene-based polymers and isoprene-based polymers are preferable andstyrene-butadiene copolymers (SBR) are more preferable.

The microstructure of SBR is not particularly limited. It is preferablethat the content of the bound styrene unit is in the range of 5 to 60%by mass and more preferably in the range of 15 to 45% by mass.

In the present invention, it is preferable that the styrene-butadienecopolymer is comprised in an amount of 50% by mass or greater in therubber component. It is more preferable that the entire rubber componentis composed of the styrene-butadiene copolymer (SBR) alone.

Examples of the diene-based monomer include 1,3-butadiene, isoprene,1,3-pentadiene, 2,3-dimethylbutadiene and 2-phenyl-1,3-butadiene. Thediene-based monomer may be used singly, as a mixture of two or more orby copolymerization with other dienes such as 1,3-hexadiene. Among thesediene-based monomers, 1,3-butadiene is preferable.

The rubber composition of the present invention comprises 10 to 200parts by mass of silica per 100 parts by mass of the polymer. The silicais not particularly limited. Examples of the silica include wet silica(hydrous silica), dry silica (silicic acid anhydride), calcium silicateand aluminum silicate. Among these compounds, wet silica is preferablesince the effect of improving the properties at break and thesimultaneous improvements in the wet gripping property and the lowrolling resistance are remarkably exhibited. It is preferable that theBET surface area is in the range of 40 to 350 mm²/g. When the BETsurface area is in the above range, the advantage is exhibited in thatthe property of reinforcing the rubber and the dispersion in the rubberare simultaneously improved. From this standpoint, it is more preferablethat the BET surface area is in the range of 8 to 300 mm²/g.

Additives which are conventionally mixed into rubber compositions can beadded as long as the effect of the present invention is not adverselyaffected. Examples of the additive include carbon black, anti-agingagents, zinc oxide, stearic acid, antioxidants and antiozonants whichare ordinarily used in the rubber industry.

The rubber composition of the present invention can be obtained bymixing the components using an open mixer such as rolls or a closedmixer such as a Banbury mixer. The rubber composition can be applied tovarious rubber products after being formed and vulcanized. Examples ofthe application include members of tires such as tire treads, undertreads, carcasses, side walls and beads and industrial products such asvibration isolation rubbers, dock fenders, belts and hoses. The rubbercomposition is advantageously used as the rubber for tire treads.

The tire of the present invention using the above rubber compositionexhibits excellent properties such as excellent abrasion resistance, asmall rolling resistance and excellent braking property and steeringstability on wet roads. As the gas used for inflating the tire, an inertgas such as the air and nitrogen can be used.

The present invention will be described more specifically with referenceto examples in the following. However, the present invention is notlimited to the examples.

The evaluations of the properties were conducted in accordance with thefollowing methods.

1. Mooney Viscosity (ML₁₊₄)

The Mooney Viscosity (ML₁₊₄/130° C.) was measured at 130° C. inaccordance with the method of Japanese Industrial Standard K6300-1994,and the obtained value is expressed as an index based on the valueobtained in Comparative Example 2, which is set at 100. The smaller theexpressed value of the Mooney viscosity, the better the processability.

2. Mooney Scorch Time

The Mooney scorch time was measured for evaluation of the stability inprocessing a rubber composition. The viscosity of an unvulcanized rubbercomposition containing components of the vulcanization system wasmeasured at 130° C. in accordance with the method of Japanese IndustrialStandard K6300-1994 using the same apparatus as that used for themeasurement of the Mooney viscosity. The time from the start ofpre-heating to the time when the viscosity increased by 5 units from theminimum value of Vm was measured. The obtained Mooney scorch time isexpressed as an index based on the value obtained in Comparative Example2, which is set at 100. The greater the expressed value of the Mooneyscorch time, the better the stability in processing.

3. Hardness

The hardness was measured in accordance with the method of JapaneseIndustrial Standard K 6253-1997, and the obtained value is expressed asan index based on the value obtained in Comparative Example 2, which isset at 100.

4. Properties at Break

The elongation at break (Eb), the strength at break (Tb) and the tensilestress at the elongation of 300% (M₃₀₀) were measured in accordance withthe method of Japanese Industrial Standard K 6251-1993, and the obtainedvalues are expressed as indices based on the values obtained inComparative Example 2, which are each set at 100.

5. Resilience

The resilience was measured in accordance with the method of JapaneseIndustrial Standard K 6255-1996 using a Dunlop tripsometer, and theobtained value is expressed as an index based on the value obtained inComparative Example 2, which is set at 100.

6. Abrasion Resistance (Rubber Composition)

The amount of abrasion at a slip ratio of 60% was measured at the roomtemperature using a Lambourn abrasion tester. The reverse of theobtained amount of abrasion is expressed as an index based on thereverse of the amount of abrasion obtained in Comparative Example 2,which is set at 100.

7. Rolling Resistance The rolling resistance of a tire was evaluated bythe measurement in accordance with the method of coasting after the tirewas rotated at a speed of 80 km/h under a load of 460 kg using arotating drum having a flat surface of steel, an outer diameter of1707.6 mm and a width of 350 mm. The obtained value is expressed as anindex based on the value obtained in Comparative Example 5, which is setat 100. The greater the expressed value, the better (smaller) therolling resistance.

8. Abrasion Resistance (Tire)

A tire was mounted to a vehicle, and the vehicle was driven for 20,000km on paved roads. The depth of grooves remaining after the driving wasmeasured, and the distance driven for abrasion of 1 mm of the tread wasobtained as a relative value. The obtained value is expressed as anindex based on the value obtained in Comparative Example 5, which is setat 100. The greater the expressed value, the better the abrasionresistance.

SYNTHESIS EXAMPLE 1

Into a 0.5 liter separable flask equipped with an inlet for nitrogengas, a thermometer, a Dimroth condenser and a dropping funnel, 80 g ofethanol, 5.46 g (0.07 moles) of anhydrous sodium sulfide and 2.24 g(0.07 moles) of sulfur were placed, and the temperature of the resultantsolution was elevated to 80° C. While the solution was stirred, 33.7 g(0.14 moles) of chloropropyltriethoxysilane ((CH₃CH₂O)₃Si—(CH₂)₃—Cl) and10.8 g (0.07 moles) of 1,6-dichlorohexane (ClCH₂—(CH₂)₄—CH₂Cl) wereslowly added dropwise. After the addition was completed, the stirringwas continued at 80° C. for 10 hours. After the stirring was completedand the solution was cooled, the formed salt was removed by filtration,and ethanol used as the solvent was removed by distillation under areduced pressured.

The obtained product was analyzed in accordance with the infraredspectroscopy (IR analysis), the ¹H-nuclear magnetic resonancespectroscopy (¹H-NMR analysis) and the supercritical chromatography, andit was confirmed that the product was a compound expressed by an averagestructural formula(CH₃CH₂O)₃Si—(CH₂)₃—S—S—(CH₂)₆—S—S—(CH₂)₃—Si(OCH₂CH₃)₃. This compound isthe compound expressed by average structural formula (I) in which R¹represents ethyl group, R³ represents n-propyl group, R⁴ representsS—(CH₂)₆—S (which is the group represented by general formula (II) inwhich R⁵ represents (CH₂)₆), p represents 0, and m represents 1. Thepurity of the compound obtained in accordance with the gel permeationchromatography (GPC analysis) was 82.5%.

SYNTHESIS EXAMPLE 2

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 1 except that 14.77 g (0.07 moles)of 1,10-dichlorodecane (ClCH₂—(CH₂)₈—CH₂Cl) was used in place of1,6-dichlorohexane used in Synthesis Example 1.

The obtained solution was analyzed in accordance with the IR analysis,the ¹H-NMR analysis and the supercritical chromatography, and it wasconfirmed that the product was a compound expressed by an averagestructural formula(CH₃CH₂O)₃Si—(CH₂)₃—S—S—(CH₂)₁₀—S—S—(CH₂)₃—Si(OCH₂CH₃)₃. This compoundis the compound expressed by average structural formula (I) in which R¹represents ethyl group, R³ represents n-propyl group, R⁴ representsS—(CH₂)₁₀—S (which is the group represented by general formula (II) inwhich R⁵ represents (CH₂)₁₀), p represents 0, and m represents 1. Thepurity of the compound obtained in accordance with the GPC analysis was84.2%.

SYNTHESIS EXAMPLE 3

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 1 except that the amount of sulfurwas changed to 4.48 g (0.14 moles).

The obtained product was analyzed in accordance with the IR analysis,the ¹H-NMR analysis and the supercritical chromatography, and it wasconfirmed that the product was a compound expressed by an averagestructural formula(CH₃CH₂O)₃Si—(CH₂)₃—S₂—S—(CH₂)₆—S—S₂—(CH₂)₃—Si(OCH₂CH₃)₃. This compoundis the compound expressed by average structural formula (I) in which R¹represents ethyl group, R³ represents n-propyl group, R⁴ representsS—(CH₂)₆—S (which is the group represented by general formula (II) inwhich R⁵ represents (CH₂)₆), p represents 0, and m represents 2. Thepurity of the compound obtained in accordance with the GPC analysis was81.0%.

SYNTHESIS EXAMPLE 4

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 1 except that the amount of sulfurwas changed to 6.72 g (0.21 moles).

The obtained product was analyzed in accordance with the IR analysis,the ¹H-NMR analysis and the supercritical chromatography, and it wasconfirmed that the product was a compound expressed by an averagestructural formula(CH₃CH₂O)₃Si—(CH₂)₃—S₃—S—(CH₂)₆—S—S₃—(CH₂)₃—Si(OCH₂CH₃)₃. This compoundis the compound expressed by average structural formula (I) in which R¹represents ethyl group, R³ represents n-propyl group, R⁴ representsS—(CH₂)₆—S (which is the group represented by general formula (II) inwhich R⁵ represents (CH₂)₆), p represents 0, and m represents 3. Thepurity of the compound obtained in accordance with the GPC analysis was80.5%.

SYNTHESIS EXAMPLE 5

Into a 2 liter separable flask equipped with an inlet for nitrogen gas,a thermometer, a Dimroth condenser and a dropping funnel, 119 g (0.5moles) of 3-mercaptopropyltriethoxysilane was placed. Under stirring,151.2 g (0.45 moles) of an ethanol solution of sodium ethoxidecontaining 20% of the effective component was added. After thetemperature was elevated to 80° C., the resultant solution was keptbeing stirred at 80° C. for 5 hours, then cooled and transferred to adropping funnel.

Into another separable flask similar to the flask used above, 69.75 g(0.45 moles) of 1,6-dichlorohexane was placed. After the temperature waselevated to 80° C., the reaction product of3-mercaptopropyltriethoxy-silane and sodium ethoxide obtained above wasslowly added dropwise. After the addition was completed, the resultantsolution was kept being stirred at 80° C. for 5 hours. The resultantmixture was cooled, and salts in the obtained solution was removed byfiltration. Ethanol and 1,6-dichlorohexane in an excess amount wereremoved by distillation under a reduced pressure. The obtained solutionwas distilled under a reduced pressure, and 137.7 g of a colorlesstransparent liquid having a boiling point of 148 to 150° C./0.005 Torrwas obtained. In accordance with the IR analysis, the ¹H-NMR analysisand the mass spectroscopy (MS analysis), it was found that the productwas the compound expressed by (CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—Cl. Thepurity of the compound obtained in accordance with the gel permeationchromatography was 97.7%.

Into another 0.5 liter separable flask similar to the flask used above,80 g of ethanol, 5.46 g (0.07 moles) of anhydrous sodium sulfide and2.24 g (0.07 moles) of sulfur were placed, and the temperature waselevated to 80° C. While the resultant solution was stirred, 49.91 g(0.14 moles) of (CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—Cl obtained above wasslowly added dropwise. After the addition was completed, the stirringwas continued at 80° C. for 10 hours. After the stirring was completedand the resultant product was cooled, the formed salts were removed byfiltration, and ethanol used as the solvent was removed by distillationunder a reduced pressure.

The obtained reddish brown transparent solution was analyzed inaccordance with the IR analysis, the ¹H-NMR analysis and thesupercritical chromatography, and it was confirmed that the product wasa compound expressed by an average structural formula(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—S₂—(CH₂)₆—S—(CH₂)₃—Si(OCH₂CH₃)₃. Thiscompound is the compound expressed by average structural formula (I) inwhich R¹ represents ethyl group, R³ represents n-propyl group, R⁴represents (CH₂)₆—S₂—(CH₂)₆ (which is the group represented by generalformula (III) in which R⁶ represents (CH₂)₆ and x represents 2), prepresents 0, and m represents 1. The purity of the compound obtained inaccordance with the GPC analysis was 85.7%.

SYNTHESIS EXAMPLE 6

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 5 except that the amount of sulfurwas changed to 4.48 g (0.14 moles).

The obtained solution was analyzed in accordance with the IR analysis,the ¹H-NMR analysis and the supercritical chromatography, and it wasconfirmed that the product was a compound expressed by an averagestructural formula(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—S₃—(CH₂)₆—S—(CH₂)₃—Si(OCH₂CH₃)₃. Thiscompound is the compound expressed by average structural formula (I) inwhich R¹ represents ethyl group, R³ represents n-propyl group, R⁴represents (CH₂)₆—S₃—(CH₂)₆ (which is the group represented by generalformula (III) in which R⁶ represents (CH₂)₆ and x represents 3), prepresents 0, and m represents 1. The purity of the compound obtained inaccordance with the GPC analysis was 84.9%.

SYNTHESIS EXAMPLE 7

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 5 except that the amount of sulfurwas changed to 6.72 g (0.21 moles).

The obtained solution was analyzed in accordance with the IR analysis,the ¹H-NMR analysis and the supercritical chromatography, and it wasconfirmed that the product was a compound expressed by an averagestructural formula(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—S₄—(CH₂)₆—S—(CH₂)₃—Si(OCH₂CH₃)₃. Thiscompound is the compound expressed by average structural formula (I) inwhich R¹ represents ethyl group, R³ represents n-propyl group, R⁴represents (CH₂)₆—S₄—(CH₂)₆ (which is the group represented by generalformula (III) in which R⁶ represents (CH₂)₆ and x represents 4), prepresents 0, and m represents 1. The purity of the compound obtained inaccordance with the GPC analysis was 81.0%.

SYNTHESIS EXAMPLE 8

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 5 except that 94.95 g (0.45 moles)of 1,10-dichlorodecane was used in place of 1,6-dichloro-hexane used inSynthesis Example 5, and a compound expressed by(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₁₀—Cl was obtained.

The synthesis was further conducted in accordance with the sameprocedures as those conducted in Synthesis Example 5 except that 57.75 g(0.14 moles) of the above compound expressed by(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₁₀—Cl was used in place of the compoundexpressed by (CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—Cl which was used in SynthesisExample 5.

The obtained reddish brown transparent solution was analyzed inaccordance with the IR analysis, the ¹H-NMR analysis and thesupercritical chromatography, and it was confirmed that the product wasa compound expressed by an average structural formula(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₁₀—S₂—(CH₂)₁₀—S—(CH₂)₃—Si(OCH₂CH₃)₃. Thiscompound is the compound expressed by average structural formula (I) inwhich R¹ represents ethyl group, R³ represents n-propyl group, R⁴represents (CH₂)₁₀—S₂—(CH₂)₁₀ (which is the group represented by generalformula (III) in which R⁶ represents (CH₂)₁₀ and x represents 2), prepresents 0, and m represents 1. The purity of the compound obtained inaccordance with the GPC analysis was 82.9%.

SYNTHESIS EXAMPLE 9

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 1 except that 16.33 g (0.21 moles)of anhydrous sodium sulfide, 20.16 g (0.63 moles) of sulfur and 21.70 g(0.14 moles) of 1,6-dichlorohexane were used.

The obtained reddish brown transparent solution was analyzed inaccordance with the IR analysis, the ¹H-NMR analysis and thesupercritical chromatography, and it was confirmed that the productcontained a compound expressed by an average structural formula(CH₃CH₂O)₃Si—(CH₂)₃—S₄—(CH₂)₆—S₄—(CH₂)₆—S₄—(CH₂)₃—Si(OCH₂CH₃)₃ as themain component. This compound is the compound expressed by averagestructural formula (I) in which R¹ represents ethyl group, R³ representsn-propyl group, R⁴ represents (CH₂)₆—S₄—(CH₂)₆ (which is the grouprepresented by general formula (III) in which R⁶ represents (CH₂)₆, andx represents 4), p represents 0, and m represents 4. The purity of thecompound obtained in accordance with the GPC analysis was 54.0%. Noprocedures were conducted for purification.

SYNTHESIS EXAMPLE 10

Into a 0.5 liter separable flask equipped with an inlet for nitrogengas, a thermometer, a Dimroth condenser and a dropping funnel, 80 g ofethanol, 5.46 g (0.07 moles) of anhydrous sodium sulfide and 2.24 g(0.07 moles) of sulfur were placed, and the temperature of the resultantsolution was elevated to 80° C. While the solution was stirred, 54.39 g(0.14 moles) of a compound expressed by an average structural formula:((CH₃CH₂O)₃Si—(CH₂)₃—S₂—(CH₂)₆—Cl) was slowly added dropwise. After theaddition was completed, the stirring was continued at 80° C. for 10hours. After the stirring was completed, the formed salt was removed byfiltration. Ethanol used as the solvent was removed by distillationunder a reduced pressured, and 50.8 g of a reddish brown transparentliquid was obtained. The obtained product was analyzed in accordancewith the IR analysis, the ¹H-NMR analysis and the supercriticalchromatography, and it was confirmed that the product was a compoundexpressed by an average structural formula(CH₃CH₂O)₃Si—(CH₂)₃—S₂—(CH₂)₆—S₂—(CH₂)₆—S₂—(CH₂)₃—Si(OCH₂CH₃)₃. Thiscompound is the compound expressed by average structural formula (I) inwhich R¹ represents ethyl group, R³ represents n-propyl group, R⁴represents (CH₂)₆—S₂—(CH₂)₆ (which is the group represented by generalformula (III) in which R⁶ represents (CH₂)₆, and x represents 2), prepresents 0, and m represents 2. The purity of the compound obtained inaccordance with the gel permeation chromatography (GPC analysis) was86.9%.

SYNTHESIS EXAMPLE 11

The synthesis was conducted in accordance with the same procedures asthose conducted in Synthesis Example 10 except that 10.92 g (0.14 moles)of anhydrous sodium sulfide, 4.48 g (0.14 moles) of sulfur and a mixedsolution of 49.91 g (0.14 moles) of a compound expressed by(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—Cl and 10.85 g (0.07 moles) of1,6-dichlorohexane was used in place of the compound expressed by(CH₃CH₂O)₃Si—(CH₂)₃—S₂—(CH₂)₆—Cl which was used in Synthesis Example 10,and 55.1 g of a brown transparent solution was obtained. The obtainedreddish brown solution was analyzed in accordance with the IR analysis,the ¹H-NMR analysis and the supercritical chromatography, and it wasconfirmed that the product was a compound expressed by an averagestructural formula(CH₃CH₂O)₃Si—(CH₂)₃—S—(CH₂)₆—S₂—(CH₂)₆—S₂—(CH₂)₆—S—(CH₂)₃—Si(OCH₂CH₃)₃.This compound is the compound expressed by average structural formula(I) in which R¹ represents ethyl group, R³ represents n-propyl group, R⁴represents (CH₂)₆—S₂—(CH₂)₆—S₂—(CH₂)₆ (which is the group represented bygeneral formula (IV) in which R⁸, R⁹ and R⁶ each represent (CH₂)₆, yrepresents 2, and z represents 2), p represents 0, and m represents 1.The purity of the compound obtained in accordance with the GPC analysiswas 85.5%.

EXAMPLE 1

A diene-based rubber (manufactured by JSR Co., Ltd.; “#1712”) in anamount of 110 parts by mass and 20 parts by mass of natural rubber weremasticated for 30 seconds by a 1.8 liter Banbury mixer under a conditionof 70 rpm and a starting temperature of 80° C. To the resultant mixture,20 parts by mass of carbon black of the ISAF grade (manufactured byTOKAI CARBON Co., Ltd.; “SIEST 7HM”), 50 parts by mass of silica(manufactured by NIPPON SILICA KOGYO Co., Ltd.; “NIPSIL AQ”), 1 part bymass of stearic acid, 1.0 part by mass of an antioxidant 6PPD(N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine) and 6.3 phr (partby mass per 100 parts by mass of the rubber component) of the compoundsynthesized in Synthesis Example 1 were mixed. After the mixing wascontinued until the temperature reached 160° C., the mixture wasdischarged and made into a sheet by rolls. The obtained mixture wasremilled for 1 minute and 30 seconds by a 1.8 liter Banbury mixer undera condition of 70 rpm and a starting temperature of 80° C. Then, themixture was discharged and made into a sheet by rolls. After theobtained mixture was sufficiently cooled to the room temperature, 3parts by mass of zinc oxide, 0.5 parts by mass of vulcanizationaccelerator DM (dibenzothiazyl disulfide), 1.0 part by mass ofvulcanization accelerator NS(N-t-butyl-2-benzothiazylsulfenamide) and1.5 parts by weight of sulfur were mixed. The resultant mixture wasmixed for 1 minute under a condition of 60 rpm and a startingtemperature of 80° C., and a rubber composition was obtained. Theresults of the evaluations are shown in Table 1.

EXAMPLES 2 TO 9

Rubber compositions were obtained in accordance with the same proceduresas those conducted in Example 1 except that compounds shown in Table 1in amounts also shown in Table 1 were used in place of the compoundsynthesized in Synthesis Example 1. The results of the evaluations areshown in Table 1.

COMPARATIVE EXAMPLE 1

A rubber composition was obtained in accordance with the same proceduresas those conducted in Example 1 except that 5.5 phr of a commercialcoupling agent (manufactured by DEGUSSA Company; “Si69”) (the structuralformula: (CH₃CH₂)O₃Si—(CH₂)₃—S₄—(CH₂)₃—Si(OCH₂CH₃)₃) was used in placeof the compound synthesized in Synthesis Example 1. The results of theevaluations are shown in Table 1.

COMPARATIVE EXAMPLE 2

A rubber composition was obtained in accordance with the same proceduresas those conducted in Example 1 except that 5.0 phr of a commercialcoupling agent (manufactured by DEGUSSA Company; “Si75”) (the structuralformula: (CH₃CH₂)O₃Si—(CH₂)₃—S₂—(CH₂)₃—Si(OCH₂CH₃)₃) was used in placeof the compound synthesized in Synthesis Example 1. The results of theevaluations are shown in Table 1.

COMPARATIVE EXAMPLES 3 AND 4

Rubber compositions were obtained in accordance with the same proceduresas those conducted in Example 1 except that compounds shown in Table 1in amounts also shown in Table 1 were used in place of the compoundsynthesized in Synthesis Example 1. The results of the evaluations areshown in Table 1. TABLE 1 Example Comparative Example 1 2 3 4 5 6 7 8 91 2 3 4 Silane compound having SE1 SE2 SE3 SE4 SE5 SE6 SE8 SE10 SE11Si69 Si75 SE7 SE9 sulfur atom* purity (%) 82.5 84.2 81.0 80.5 85.7 84.982.9 86.9 85.5 — — 81.0 54.0 amount (phr) 6.3 6.6 7.0 7.5 7.2 7.5 8.28.5 9.3 5.5 5.0 8.3 10.3 Mooney viscosity (ML₁₊₄) 90 87 100 109 104 105102 100 95 115 100 111 118 Mooney scorch time 101 100 90 60 95 94 98 9998 62 100 71 64 Hardness 103 100 104 104 104 108 101 102 103 104 100 110105 Properties at break elongation at break (Eb) 97 106 93 75 95 88 10592 94 77 100 72 72 strength at break (Tb) 96 108 98 87 98 98 103 104 10695 100 85 81 tensile stress at 300% 104 101 110 128 105 120 101 116 118115 100 131 125 elongation Resilience 106 107 107 115 112 112 110 115120 120 100 115 112 Abrasion resistance 100 103 100 87 109 109 108 109112 70 100 75 61 (rubber composition)*SE: The compound of Synthesis Example

As clearly shown in Table 1, the compositions of Examples exhibitedsmaller Mooney viscosities, greater resilience and more excellentabrasion resistance, and the physical properties were more excellentlybalanced than those of compositions of Comparative Examples.

EXAMPLE 10

A tire was prepared in accordance with the conventional process usingthe rubber composition of Example 3 for the tread. The size of the tirewas 205/65R15, and the size of the rim was 15×6JJ. The inner pressurewas adjusted at 220 kPa. The tests of rolling resistance and abrasionresistance of the tire were conducted using the prepared tire. Theresults are shown in Table 2.

EXAMPLE 11

A tire was prepared and evaluated in accordance with the same proceduresas those conducted in Example 10 except that the amount of the silanecompound having sulfur atom in the rubber composition of Example 3 waschanged to 5.0 phr. The results are shown in Table 2.

EXAMPLE 12

A tire was prepared and evaluated in accordance with the same proceduresas those conducted in Example 10 except that the rubber composition ofExample 9 was used. The results are shown in Table 2.

COMPARATIVE EXAMPLE 5

A tire was prepared and evaluated in accordance with the same proceduresas those conducted in Example 10 except that the rubber composition ofComparative Example 2 was used. The results are shown in Table 2. TABLE2 Comparative Example 10 Example 11 Example 5 Example 12 Rubbercomposition rubber rubber rubber rubber composition compositioncomposition of composition of of Example 3 Comparative of Example 3(modified) Example 2 Example 9 Silane compound having SE3 SE3 Si75 SE11sulfur atom* purity (%) 81.0 81.0 — 85.5 amount (phr) 7.0 5.0 5.0 9.3Rolling resistance (index) 106 105 100 108 Abrasion resistance (tire)102 101 100 106*SE: The compound of Synthesis Example

As clearly shown in Table 2, the tires of Examples exhibited moreexcellent rolling resistance and abrasion resistance than those of thetire of Comparative Example.

INDUSTRIAL APPLICABILITY

The rubber composition of the present invention has a small viscosity inthe unvulcanized condition and provides excellent dispersion of silica.When this composition is used for the tread member of a tire, a tireexhibiting excellent abrasion resistance, a small rolling resistance andimproved braking property and steering stability on wet roads can beobtained.

1. A rubber composition which comprises, per 100 parts by mass of apolymer, 10 to 200 parts by mass of silica and 1 to 30 parts by mass ofa silane compound having sulfur atom represented by average structuralformula (I):(R¹O)_(3-p)(R²)_(p)Si—R³—S_(m)—R⁴—S_(m)—R₃—Si(R²)_(p)(OR¹)_(3-p)  (I)wherein R¹ and R² each represent a hydrocarbon group having 1 to 4carbon atoms, R³ represents a divalent hydrocarbon group having 1 to 15carbon atoms, p represents an integer of 0 to 2, m represents a numberof 1 or greater and smaller than 4, which may be an average of numbers,and R⁴ represents a divalent functional group represented by one offollowing general formulae (II) to (IV):S—R⁵—S  (II)R⁶—S_(x)—R⁷  (III)R⁸—S_(y)—R⁹S_(x)—R¹⁰  (IV) wherein R⁵ to R¹⁰ represents a linear orbranched divalent hydrocarbon group having 1 to 20 carbon atoms, adivalent aromatic group or a divalent organic group having a hetero atomwhich is not sulfur atom or oxygen atom, R⁵ to R¹⁰ may represent a samegroup or different groups, and x, y and z each represent a number of 1or greater and smaller than 4, which may be an average of numbers.
 2. Arubber composition according to claim 1, wherein m represents 1 inaverage structural formula (I) representing the silane compound havingsulfur atom.
 3. A rubber composition according to claim 1, wherein x, yand z each represent a number of 2 or greater and 3 or smaller, whichmay be an average of numbers, in general formulae (III) and (IV)representing the divalent functional group.
 4. A rubber compositionaccording to claim 1, wherein R⁴ represents a divalent functional grouprepresented by general formula (IV) in average structural formula (I)representing the silane compound having sulfur atom.
 5. A rubbercomposition according to claim 1, wherein, in average structural formula(I) representing the silane compound having sulfur atom, R⁴ represents adivalent functional group represented by general formula (IV) in whichR⁸, R⁹ and R¹⁰ each represent hexylene group.
 6. A rubber compositionaccording to claim 1, wherein a purity of the silane compound havingsulfur atom is 60% or greater at a time when the silane compound havingsulfur atom is mixed to form the rubber composition.
 7. A rubbercomposition according to claim 1, wherein, at a time when the silanecompound having sulfur atom is mixed to form the rubber composition, acontent of silane compounds having sulfur atom and three or more siliconatoms in one molecule is 30% by mass or smaller of the rubbercomposition.
 8. A rubber composition according to claim 1, wherein a BETsurface area of the silica is 40 to 350 m²/g.
 9. A rubber compositionaccording to claim 1, wherein the polymer is a diene-based rubber.
 10. Atire which comprises a member comprising a rubber composition describedin claim
 1. 11. A tire according to claim 10, wherein the member is atire tread.
 12. A rubber composition according to claim 2, wherein, at atime when the silane compound having sulfur atom is mixed to form therubber composition, a content of silane compounds having sulfur atom andthree or more silicon atoms in one molecule is 30% by mass or smaller ofthe rubber composition.